1. Field of the Invention
The present invention relates to a photodiode of the type which comprises a semiconductor substrate, reflectors which form several optical resonators in the semiconductor substrate, and electrodes for the supply of current thereto and for the removal of electrical signals which are based on radiation reception in a single resonator or in several of the resonators, whereby, for the substrate, a material having a relatively low absorportion coefficient for the radiation to be detected and having good suitability for semiconductor-element integration is selected.
2. Description of the Prior Art
From the German published application No. 28 28 195, corresponding to U.S. Pat. No. 4,202,000, fully incorporated herein by this reference, a semiconductor diode is known which is also to be utilized as a photodiode. This diode may be constructed with an optical Fabry-Perot resonator and may be employed as a laser diode. Oppositely disposed surfaces of the semi-conductor chip serve as the mirror of the resonator. A high sensitivity to the radiation to be detected in the photo diode is achieved through the utilization of an avalanche effect.
An integrated semiconductor component is known from the Bell Laboratories Record, 1981, pp. 38-45, which consists of a laser and a detector which are both realized in the same semiconductor chip. Other details concerning the construction of the detector are not provided.
In the prior German patent application No. P 32 05 461.0, a photodiode is disclosed having an optical resonator serving for increasing absorption. The basis for this photodiode is to provide a structure for a photodiode which is of such a type which can be realized as an integrated component of a semiconductor chip in which there is at least an additional semiconductor function, particularly a laser. The photodiode corresponding to this earlier application is suitable, in particular, for silicon for which a wellknown integration technology has been developed. For optical purposes, however, silicon has the disadvantage that its band gap energy lies in the near infrared range where the application of optical means is of particular interest. Precisely near the band edge for wavelengths greater than equal to 1.1 .mu.m the silicon has only a low specific absorption and is not considered utilizable for this range for photodiodes.
A comparable case exists for gallium arsenide as a material of the semiconductor chip; namely, for the combination of a laser with a photodiode, or, for the frequency range of the laser radiation to be generated in the gallium arsenide, the latter gallium arsenide is not useable for a photodiode of conventional construction due to lack of sufficient absorption behavior.
The solution suggested in the German application No. P 32 05 461.0 is that of constructing the photodiode in a semiconductor material having an absorption coefficient which is too low per se for photodiode, as an optical Fabry-Perot resonator, preferably as an asymmetrical resonator.